In a variety of fields including cosmetics, household agents and parting agents, it is required that an organopolysiloxane having a high degree of polymerization or organopolysiloxane having a branched silicone chain be available in emulsion form. However, when such organopolysiloxane is directly emulsified, a particle size of several microns becomes the limit. So studies were made on the preparation method via emulsion polymerization. For example, it is known from Patent Documents 1 and 2: JP-B S34-2041 and JP-B S41-13995 that cyclic siloxane oligomers are emulsified before emulsion polymerization is conducted in the presence of strong acids or strong bases.
Recently, octamethylcyclotetrasiloxane becomes a matter of concern as environmental loading substance. Samples having a reduced content of octamethylcyclotetrasiloxane are required. It is known that the siloxanes in the above-cited patent documents contain 40,000 ppm or more of octamethylcyclotetrasiloxane. Studies have been made on the method of suppressing the amount of octamethylcyclotetrasiloxane formed.
As one exemplary method, it is known from Patent Document 3: JP 3145394 that a condensation reactive organopolysiloxane having a silanol group at the end of the molecular chain and containing up to 5,000 ppm of a non-condensation reactive organosiloxane oligomer of up to 20 silicon atoms is subjected to emulsion polymerization at 40° C. or lower for a polymerization time within 40 hours. However, an ordinary nonionic surfactant of the structure having a hydroxyl group at the end, which is used to enhance the stability of emulsion, inhibits condensation of silanol. Even after emulsion polymerization is continued for 40 hours, the ultimate viscosity is several million mm2/s. The emulsion polymerization time must be further prolonged before a higher degree of polymerization can be reached.